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Combining the Effects of Climate Change and Agriculture on Mammal Populations

In concert with the effects of climate change, some agricultural practices are having an unanticipated combined effect on ecosystems and biodiversity. Brodie (2016) showed that agricultural expansion coupled with climate change will have a more intense effect on the mammals in the extremely biodiverse region of Southeast Asia than either cause alone. Rising temperatures allow farmers to expand the growing region for cold-sensitive crops like the non-native oil-palm trees. While rising temperatures themselves do not disrupt the region’s mammalian species, the destruction of native forests in place of new agricultural areas would reduce mammal ranges by 47-67% by 2070. This is 3-4 times the reduction predicted considering direct effects from conversion of natural forest to plantations alone. In this study Brodie calls for a greater investigation of the combined effects of climate change and agriculture on biodiversity.

Brodie investigates the interaction of land-use changes and climate change in equatorial Southeast Asia, one of the planet’s most biodiverse areas, which includes the five subregions Borneo, Sumatra, Malaya, Java, and Bali. A particular threat to biodiversity in this region is the non-native African oil palm, the production of which is expanding rapidly as global demand for biodiesel and edible oil products increases. Production is currently limited to the tropical lowlands, however as the region warms due to the effects of climate change, the zone where oil palm can be grown on a large scale (in monoculture plantations) will expand into higher elevations.

Current climate data were taken from WorldClim Global Climate Data, and climate projections up to the year 2070 were taken from the most recent set of general circulation models published in the Intergovernmental Panel on Climate Change’s 5th Assessment Report. Range maps for 286 native mammalian species from the International Union for Conservation of Nature were used to determine habitable zones for each species of mammal.

These data combined with topological data for the region and used in environmental niche modeling, or ENM, produced virtual ‘maps’ predicting future regions of oil-palm cultivation as well as the zones of habitability for the mammals. Brodie conducted five projections of the species’ living zones into 2070—two of which considered the effects of climate change alone (one low-emission prediction and one high-emission prediction), one projection which considered only the expansion of oil-palm to all currently available zones, and two more which combined the effects of climate and land-use changes. Brodie found that climate change alone did not significantly reduce the area of environmental suitability for most species. Oil-palm expansion limited to current suitability zones generates an average 15.9% loss of suitable area for mammals. The combination of climate change and oil palm expansion produced the strongest negative impact, generating an average 47-67% loss of habitable zones for mammals.

This analysis is necessarily incomplete, as there are many variables particular to each species—such as ability to shift habitat or complete reaction to warming temperatures—that cannot be accounted for. Additionally, future distribution of crops will be subject to the variable forces of market demand and human-imposed constraints. However, it is reasonable to assume an extensive expansion of oil palm into all available areas, as global demand for edible-oil products is expected to double by 2050.

The results of this analysis indicate that studying interactive effects of climate change and other changes such as land-use could provide much more valuable information than considering the effects separately or additively. Conversion of ecosystems into agricultural land—especially into large-scale monoculture farms—may be the most significant global driver of biodiversity decline. Measures to protect natural ecosystems over agriculture—such as enforced natural forest areas or returning agricultural land to native communities—would provide some deeply needed security for these ecosystems, which may be more at risk from the combined effects of climate change and agricultural practices than previously thought.